Micro-reflectors on a substrate for high-density LED array

ABSTRACT

The present invention provides an optical array module that includes a plurality of semiconductor devices mounted on a thermal substrate formed with a plurality of openings that function as micro-reflectors, wherein each micro-reflector includes a layer of reflective material to reflect light. Such material preferably is conductive so as to provide electrical connection for its associated semiconductor device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/084,466, filed Mar. 18, 2005, which claims the benefit of U.S.Provisional Patent Application No. 60/554,628, filed Mar. 18, 2004, allof which are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to high-density light emitting diode (LED) arraysand, more particularly, to an LED array that has improved collection andcollimation of light.

High-density UV LED arrays may be used for a variety of applications,including, e.g., curing applications ranging from ink printing to thefabrication of DVDs and lithography. Many such applications require ahigh optical power density at the working surface. However, such powerdensity tends to be unavailable from a typical LED as such LED alonegenerally is characterized by light distribution that is undesirablydivergent.

For example, FIG. 1 is a graphic illustration showing radiationdistribution for two typical LEDs 22, 24 mounted on a surface 26 withoutrefractive or reflective optics. Ideally, particularly for applicationsas above described, the light from the LEDs 22, 24 would be distributedsubstantially 90 degrees from substrate 26. However, the LEDs 22, 24will typically emit highly divergent light. In FIG. 1, this isillustrated by curves 28 and 30. Curve 28 is a representative example ofradiation distribution from first LED 22 and curve 30 is arepresentative example of radiation distribution from second LED 24.Because much of radiation from LEDs 22, 24 is emitted at highly obliqueangles, the optical power density falls off relatively quickly as afunction of the distance of the work surface from the LED. This fall offis graphically illustrated in FIG. 2 for an LED array without refractiveor reflective optics.

Typically, the performance illustrated by FIGS. 1 and 2 may vary as thesystem is changed. For example, the performance would tend to vary ifdifferent LEDs are used and if the LEDs are placed in different arrays(e.g., depending on the number and spacing of LEDs in the array). In anycase, particularly for the aforementioned applications, divergence andfall off similar to that illustrated by FIGS. 1 and 2 will tend to beundesirable.

To achieve the optical power density typically required in theaforementioned applications, an LED array exhibiting such divergencecould and often is located physically close to the work surface. Thatis, the proximity of the array to the work surface would be closer thanif the array did not exhibit such divergence. Moreover, such closeproximity generally is undesirable, including because it will typicallynecessitate mechanical changes to tooling and/or shielding toaccommodate such proximity. However, locating the LED array too far fromthe work surface may diminish the optical power density to undesiredlevels, which levels may hinder or preclude proper operation in theapplication.

There are known methods of achieving higher optical power density. Forexample, some LEDs are used with Lambertian optical outputs to achieve ahigher optical power density. However, such devices are less efficientin electrical to optical conversions as well as being less thermallyefficient. Another method of achieving higher optical power density isshown if FIG. 3 in which an array of refractive optical elements 32 islocated above an array of LEDs 34 in which each LED 34 is associatedwith an optical element 32. Each optical element 32 collects andcollimates the light from its associated LED 34. However, this method isinefficient because light from LEDs is highly divergent causing much ofthe light to fall outside the numerical aperture of the lenses. Thenumerical aperture of a lens is defined as the sine of the angle betweenthe marginal ray (the ray that exits the lens system at its outer edge)and the optical axis multiplied by the index of refraction (n) of thematerial in which the lens focuses. In order to more effectively collectand collimate the light the optical component must have a very highnumerical aperture resulting in a lens that has a very large diameterand a very short focal length. In practice, it is not possible tomanufacture a refractive optical element that collects all of the lightfrom an LED because that would require the angle between the opticalaxis and the marginal ray to be 90 degrees, implying a lens of either azero focal length or an infinite diameter.

Another common approach to collecting and collimating light from an LEDis to use a parabolic reflector as shown in FIG. 4. AN LED 36 is mountedin parabolic reflector 38 so that light rays 40 emitted from LED 36 arecollected and collimated. Unlike refractive optics, reflective opticsgenerally collect all the light from the LED, even at very highlyoblique angles. However, known reflective optics are not used in atightly packed or dense array because of their size. For example, atypical application of such reflective optics is with LED-mountedflashlights in which the reflective optic collimates light from only asingle LED.

Additionally, in known optical devices the reflector is separate fromthe electrical circuitry of the device. For example, such devicestypically utilize a macro-reflector for an entire array of LEDs. Theoptical efficiency of these devices is lowered because each LED does nothave an associated reflector. Additionally, the volume of space requiredfor the macro-reflector is very large which increases the cost ofmanufacturing.

SUMMARY OF THE INVENTION

The present invention provides an LED array using micro-reflectors. Themicro-reflectors, generally, collect and collimate light from the LEDarray. In doing so, the micro-reflectors enhance the array's opticalpower. In typical applications, the LED array benefits from suchenhanced optical power in that it may be physically located further awayfrom a work surface and yet deliver optical power sufficient to enableproper operation.

In one aspect, the present invention provides a dense LED array in whicheach LED of such array is mounted in a micro-reflector. Accordingly, anarray of micro-reflectors. The micro-reflectors typically are formed ina substrate. Preferably, the substrate is of a material that iselectrically insulating. Preferably, the substrate is also thermallyconductive.

In one embodiment, the substrate is a crystalline silicon having definedcrystallographic axes along which the substrate is etched to formopenings in the substrate. These openings have walls with acharacteristic slope, so as to have a substantially truncated pyramidalshape. The openings are metallized and otherwise structured to defineselected circuits. The resulting substrate has openings formed in adense array, which openings are coated with a reflective material sothat the openings function as micro-reflectors. Preferably, thereflective material is also electrically conductive so that the openingsalso function as electrical connectors (e.g., if coupled to power or toground).

In this embodiment, one or more LEDs are mounted within eachmicro-reflector and wired into a circuit on the substrate. The LEDs ofthe array is electrically connected to a power source, with themicro-reflector preferably providing electrical connection to theassociated LEDs (e.g., the reflector being coupled to either power or toground).

The substrate may be formed of any size and the LEDs arranged in anydesired dense configuration required for a particular application.

In another embodiment, a dense LED array is provided in which an arrayof micro-reflectors is formed using a substrate of other than silicon,such as an insulator, a semiconductor, a conductor, or combinations ofone or more of these or other materials. As examples, the substrate maybe glass, ceramic, diamond, SiC, AlN, BeO, Al2O3, or combinations ofthese or other materials.

Micro-reflectors may be formed using various technologies. As examples,the micro-reflectors may be formed using lithographical technology,machining, stamping, casting, forging, or other processes, orcombinations of one or more of these. To illustrate, micro-reflectorsmay be machined into the substrate and/or otherwise formed (e.g., suchmachining via lasers and/or plasma). To further illustrate,micro-reflectors may be formed by a combination of etching, togetherwith machining or other technology. In this illustration, a substratemay be etched to form openings. Each opening is then machined to adesired shape, such as a parabolic shape. Such machining may beperformed before or after the substrate, including the openings, iscoated with a reflective material.

Micro-reflectors may be formed having various shapes. Generally, theshape is selected so as to optimize the optical power density. Whileparabolic micro-reflectors are typical, micro-reflectors may have othershapes. Moreover, the shapes may be varied within any particular array.As such, the micro-reflectors in the array may be patterned.

The present invention provides an array module that includes a pluralityof semiconductor devices mounted on a substrate formed with a pluralityof openings that function as micro-reflectors, wherein eachsemiconductor device or multiple devices is associated with amicro-reflector, each micro-reflector including a layer of reflectivematerial to reflect light. Preferably, such reflective material iselectrically conductive and coupled so as to provide electricalconnection for its associated semiconductor device.

The present invention further provides a method of manufacturing anarray module comprising the steps of providing a substrate, forming aplurality of openings in the substrate, providing a layer of reflectivematerial in each opening, and mounting a semiconductor device withineach opening so that the layer of reflective material in each openingreflects light. Preferably such material is electrically conductive andcoupled so as to provide electrical connection for its associatedsemiconductor device.

The present invention provides for a method of manufacturing an arraymodule in which a substrate is metallized. Metal circuits are structuredon the metallized substrate and the substrate is then etched to formopenings. The openings are then metallized to form micro-reflectors thatreflect light (and, preferably, that provide electrical connection foran associated semiconductor device). This enables the formation offeatures in the electrical circuit separately from the etching andplating tasks associated with forming the micro-reflectors.

The present invention further provides an optical device thatincorporates a reflector into the electrical circuitry of the opticaldevice so as to obtain higher optical efficiency with lower costs.

These and other embodiments are described in more detail in thefollowing detailed descriptions and the figures.

The foregoing is not intended to be an exhaustive list of embodimentsand features of the present invention. Persons skilled in the art arecapable of appreciating other embodiments and features from thefollowing detailed description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows radiation distribution for two LEDs without refractive orreflective optics.

FIG. 2 shows a graph of an example of power drop-off as a function ofdistance from the LED array for a specific array.

FIG. 3 shows an example of prior art refractive lenses used to collectand collimate light from an array of LEDs.

FIG. 4 shows a common approach of collecting and collimating light froman LED with a parabolic reflector.

FIG. 5 is an enlarged top view of a portion of an LED array according toone aspect of the present invention.

FIG. 6 is a view of the LED array of FIG. 5 taken along line 6-6.

FIG. 7 is a top view of the substrate formed with an array of pocketsaccording to one aspect of the invention.

FIG. 8 is an enlarged partial top view of a portion of the substrate ofFIG. 7.

FIG. 9 is an enlarged partial side view of a portion of the substrate ofFIG. 7.

FIG. 10 is a graphic illustration showing the improved directionality oflight from an LED with reflective pockets of the substrate of theinvention.

FIG. 11 is a graph of calculated power as a function of distance for anLED array arranged on a grid with 1 mm center-to-center spacing.

FIG. 12 is an alternative embodiment of the invention with parabolicmicro-reflectors.

FIG. 13 is yet another embodiment of the invention in which themicro-reflectors are formed by a combination of etching and machining.

FIG. 14 is another embodiment of the invention incorporating an array ofmicro-lenses.

DETAILED DESCRIPTION OF THE INVENTION

Representative embodiments of the present invention are shown in FIGS.5-14, wherein similar features share common reference numerals.

In a basic embodiment, an LED array employs micro-reflectors. Themicro-reflectors, generally, collect and collimate light from the LEDarray. In doing so, the micro-reflectors enhance the array's opticalpower. In typical applications, the LED array benefits from suchenhanced optical power in that it may be physically located further awayfrom a work surface and yet deliver optical power sufficient to enableproper operation.

FIG. 5 shows a portion of a dense LED array 50 that may be used forapplications requiring high optical power density at the workingsurface. Such applications may include, for example, curing applicationsranging from ink printing to the fabrication of DVDs and lithography.One such LED array is shown and described in U.S. patent applicationSer. No. 10/984,589, filed Nov. 8, 2004, the entire contents of whichare hereby incorporated by reference for all purposes.

Array 50 includes a substrate 52 having micro-reflectors 54 formedtherein. An LED 56 is mounted within each micro-reflector 54 in a mannerknown by those skilled in the art. Although the figures show only oneLED associated with a micro-reflector each micro-reflector may beassociated in one or more LEDs, such as one of each red, green, andblue, or other colors, or any combination thereof. One type of LEDsuitable for use is a P/N C395-XB290-E0400-X, manufactured by Cree,Inc., located in Durham, N.C., USA.

Each LED 56 may be mounted using various technologies. The technologiesinclude, as examples, bonding using a conductive adhesive, soldering, oreutectic bonding.

Each LED 56 is electrically connected to a power source (not shown)through a lead line 58 connected in a known manner to a wire bond pad 60on substrate 52.

In this embodiment, each row R(1), R(2), R(3) is electrically isolatedby an isolation band 61. It is to be understood, however, that the arraymay provide isolation on a basis other than by row. For example, eachLED may be electrically isolated from all other LEDs in the array, orfrom the immediately surrounding LEDs (e.g., while being electricallyconnected with selected LEDs adjacent to such surrounding LEDs), or fromsome other selection of LEDs. In this way, electrically connected LEDsmay be provided in a selected pattern throughout or in one or more partsof the array. This isolation/connection may be useful in controllingheating of the LED array, e.g., by selectively reducing power to, oreven shutting down individual LEDs or one or more groups of the LEDs, soas to counter undesirable heating. Heating of LED arrays, and methods tohandle such heating, including the selective control of power providedto one or more LEDs in such array, are shown and described in U.S.patent application titled “DIRECT COOLING OF LEDS,” Ser. No. 11/083,525,filed Mar. 18, 2005, claiming priority to U.S. Provisional ApplicationSer. No. 60/554,632, filed Mar. 18, 2004, the entire contents of whichapplication are hereby incorporated by reference for all purposes.

Each micro-reflector 54 includes a layer 62 of reflective and,preferably, electrically conductive material both to reflect light fromand to complete a circuit to electrically connect (e.g., power) anassociated LED 56. Various materials may be employed that are bothoptically reflective and electrically conductive and that can be bondedto electrically. As examples, these materials include copper, aluminum,gold, and silver, or combinations thereof or alloys therewith. Thisconstruction provides micro-reflectors 54 that reflect light from anassociated LED 56 and that are incorporated into the conductivecircuitry to provide electrically connection (e.g., to power) for anassociated LED 56. Although it is preferred that the materials used toprovide the micro-reflectors are used to both reflect and to provideelectrical connection, it is understood that the materials may be usedfor only one such purpose, e.g., to reflect light, without departingfrom the principles of the invention.

Substrate 52 is preferably a 1-0-0 crystalline silicon wafer. This waferhas defined crystallographic axes that are determined by silicon'scrystalline lattice. One of the consequences of silicon's crystallinenature is that etching of silicon can be made to progress preferentiallyalong some crystallographic axes as compared to others. As a result,when the surface of a silicon wafer is properly oriented, masked toexpose the surface to be etched, and placed in an etching solution (suchas potassium hydroxide or hydrofluoric acid), openings are etched in thesilicon having walls with a characteristic slope, typically of about54.7 degrees.

Substrate 52 preferably is fabricated using a cleaned and polished 1-0-0silicon wafer. The wafer surfaces generally are super cleaned to removecontamination. Known cleaning methods include a hydrofluoric acid soakfollowed by one or more aluminum hydroxide soaks, multiple dump rinses,and a distilled water spin rinse dry in heated dry nitrogen.

A layer (e.g., silicon nitride) is applied to the substrate 52 usinggenerally understood methods, e.g., vapor deposition or plasma enhancedvapor deposition. This layer can be, for example, about 2,400 angstroms.This layer is then coated with photoresist. It is necessary toselectively remove photoresist from wafers prior to etching into thesilicon. To do so, the photoresist imaged or exposed with a mask andselected portions of the photoresist are removed using an oxygen plasma(12 cc/min. oxygen flow at 360 watts) or resist stripper (such asShipley 1112 A), followed by several distilled water rinses. By removingselected photoresist, portions of the substrate's surface are exposedwhere openings that will become the micro-reflectors are desired. In oneembodiment, the silicon surface is prepared to expose a plurality ofsquare shapes having sides measuring about 700 microns (0.028 in.) andspaced apart in a center-to-center spacing of about 800 microns (0.032in.).

The exposed portions of the layer (e.g., silicon nitride) are thenetched. Silicon nitride can be etched with buffered hydrofluoric acid(BHF), which will not attack silicon. An alternative to BHF is reactiveion etch (RIE). One example of the RIE for this application is to etchfor 90 seconds at 150 watts and 50 standard cubic centimeters per minuteSulfur Hexafluoride (SF₆) at 100 mTorr vacuum. The silicon nitrideopenings are etched until the base silicon wafer is fully exposed andshiny.

The silicon is then etched. For example, potassium hydroxide (KOH) maybe employed as a wet etch that attacks silicon preferentially in the1-0-0 plane, producing a characteristic anisotropic V-etch withsidewalls that form about a 54.7 degree angle with the surface (35.3degree from the normal). Adding 1 percent isopropyl alcohol to the KOHsolution will lower the surface tension of the solution, typicallyresulting in smoother etched walls.

The speed of the etch can be adjusted by those skilled in the art. Toillustrate, the etch rate can be about 750 angstroms per minute at roomtemperature using a potassium hydroxide (KOH) solution of 400 grams ofKOH per liter of distilled water. At 52 degrees C. the etch rate isabout 14 microns per hour.

In this etch process, the etch rate of the silicon nitride layer isabout 300 times slower than the etch rate of the silicon. While this mayprovide sufficient control to protect the silicon nitride, it may benecessary to monitor and adjust the thickness of the silicon nitridelayer to ensure that it is properly masking during the entire basesilicon wafer etching.

The result is a substrate 66 as seen in FIGS. 7-9, having an array ofopenings 68. In this embodiment, openings 68 are arranged in a denselypacked array in a center-to-center spacing of about 800 microns (0.032in.). Each micro-reflector is formed in a truncated pyramidal shape inwhich opening 68 has sides having dimensions 70 of about 700 microns(0.028 in.) square. Openings 68 have sidewalls 72 that slope to a base74 at an angle of about 54.7 degrees from a horizontal plane. Base 74has a dimension 76 of about 346 microns (0.014 in.) square and openingshave a depth (D) of about 250 microns (0.010 in.). These dimensions aremerely illustrative and the invention is not limited to an opticaldevice with these dimensions. For example, an optical device may beconstructed and arranged so that the micro-reflectors have acenter-to-center spacing of about 3 mm or less.

Substrate 52, including the openings 68, is then metallized. In doingso, typically several thin film layers are used. Preferably, the filmlayers are applied using generally understood methods, e.g., vapordeposition or plasma enhanced vapor deposition. Various layers andcombinations of layers may be used. Generally, however, each such layer,and the layer combinations, are selected to address one or more variousdesirable performance characteristics, including as examples: to reflectlight (including light of selected wavelength(s)), to provide electricalconnection(s), to provide electrical insulation (including circuitisolation), to provide adhesion of the layers to the substrate, tocombat metal migration, and to enhance mounting of the LED in themicro-reflector.

In one possible layer combination, a dielectric coating of about 1000angstroms of silicon dioxide is applied to isolate the conductivecircuit from the semiconductor. An adhesion layer of about 100-500angstroms of titanium is then applied to improve adhesion of the metallayers. Next, a barrier metal layer of about 100-500 angstroms of nickelis applied to prevent metal migration between the layers. Then, a lightreflecting and electrically conducting layer is applied to form both anoptical reflector and an electrical circuit. For UV light, this layercan be about 1-10 microns of silver or aluminum and, for visible light,this layer can be about 1-10 microns of gold.

Another possible layer combination is to use 1,000 angstroms of silicondioxide to isolate the conductive circuit followed by 1,000 angstroms oftitanium to improve adhesion of the metal layers. A barrier layer ofabout 1,000 angstroms of nickel may be applied to prevent metalmigration between the layers. Generally, it is not desirable to useheavy nickel layers where the tendency of the nickel is to cause peelingof the metal.

The nickel layer may then by coated with about 6 microns of silver toform the reflective and electrical conductive layer. The nickel andsilver material constitute an electrical conductor enabling use ofbonding techniques common to fabrication of semiconductor devices, e.g.,wire bonding, such as with Au, Ag, Al, thermal adhesives and solderingprocesses. The heavy silver layer also helps to carry relatively highelectrical currents, so as to optimize optical power generation,particularly of UV light. Although it is preferred that the materialsused to provide the micro-reflectors are used to both reflect and toprovide electrical connection, it is understood that the materials maybe used for only one such purpose, e.g., to reflect light, withoutdeparting from the principles of the invention.

After the metallization process described above, isolation band 61 isformed so as to form the electrical circuits on the metallizedsubstrate. There are various known methods generally to provideelectrical isolation among selected circuit elements or, specifically,to form isolation band 61 to form circuits on metallized substrates. Inone example, the isolation is provided via subtractive techniques toremove selected portions of the metal and thereby electrically isolatevarious circuit elements. In this example, a laser processes may beemployed to cut through the selected portion(s) of the metal and,typically, slightly into the silicon. As well, photolithographicprocesses may be used (e.g., including using photoresist, masking,developing, and etching, such as via a wet or plasma etch) to remove theselected portion(s) of the metal. While the laser processes tend to beflexible and relatively easy to change/adjust as to locations andgeometries, the photolithographic process uses existing, well-understoodand typically cost-effective fabrication systems. Generally, any ofthese or other process, alone or in combination, will be suitable.

Generally, one or more LEDs are mounted within each micro-reflector andelectrically connected. The LEDs are electrically connected to a powersource. Preferably, each micro-reflector provides electrical connectionto its associated LEDs (e.g., the reflector being coupled to eitherpower or to ground). Such connection is enabled by use of the metallayers (as described above). In doing so, the metal layers provide asource (or return) electrode. The LEDs typically are also electricallyconnected to an other feature that provides a return (or source)electrode, so as to complete an electrical circuit. As example thisother feature may be the wire bond pad 60 on the surface of thesubstrate, connected via lead line 58, as described above with referenceto FIGS. 5 and 6. In the alternative, this other feature may be providedby the substrate or other material providing the base of themicro-reflector. In such alternative, particularly if the reflectivemetal layer(s) of the micro-reflector are an electrode, the substrate(and/or other material) is electrically isolated from the associatedmetal layers of the micro-reflector using one or more appropriatedielectric layers. Moreover, if the micro-reflector is formed in anopening fabricated within a material applied above the substrate (suchthat the base of the micro-reflector is outside the substrate), thatmaterial may provide the other electrode with or without using thesubstrate in making the return (or source) connection (e.g., theelectrical connection may be made via the substrate or via conductivefeatures fabricated on the substrate).

Metallization on the back of the silicon provides for solder attach of,e.g., a supporting structure (not shown), a heat sink (not shown),and/or other circuitry (not shown). The metallization may be a heavysilver layer. This silver layer can be replaced by a flash of gold toprotect the nickel. The flash of gold keeps the nickel from oxidizingfor improved solderability. The gold will go into solution in thesolder. Minimizing the gold thickness will minimize cost while ensuringsolderability and will minimize gold embrittlement potential in thesolder joint connection between the substrate and, e.g., the supportingstructure. Once the substrate has been fully processed the LEDs aremounted and bonded in a known manner (discussed above) to complete theLED array.

The LED array 50, employing micro-reflectors, provides improvedcollection and collimation of light emitted from the LEDs. FIG. 10 showsa graphic illustration of improved directionality in which curve 80represents a generalized angular irradiance distribution of an LEDwithout the use of optics (see also FIG. 1). Curve 82 represents theangular distribution of an LED after mounting into a micro-reflectorformed by anisotropic etching 350 microns deep in a silicon substrate.FIG. 11 is a graphic illustration showing the calculated power as afunction of distance for an array of LEDs mounted in the substratearranged in a grid with a 1 mm center-to-center spacing. As seen bycomparing the graphic illustrations of FIG. 2 and FIG. 11, the opticalpower density of an LED array absent micro-reflectors drops by about 50%at a distance of only about 0.5 cm (FIG. 2), whereas the optical powerdensity of an LED array employing micro-reflectors drops by about 50% ata distance of about 2.6 cm (FIG. 11). Accordingly, an LED arrayemploying micro-reflectors (as described herein) typically can belocated relatively further away from a work surface than can an LEDarray without such micro-reflectors, while maintaining a substantiallyequivalent optical power density and, thus, enabling proper performance,particularly in certain applications.

Micro-reflectors may be formed having various shapes. Generally, theshape is selected so as to optimize the optical power density. Whileparabolic micro-reflectors are typical, micro-reflectors may have othershapes. Moreover, the shapes may be varied within any particular array.As such, the micro-reflectors in the array may be patterned. Toillustrate, the etched micro-reflectors in FIGS. 7-9 are shown having aninverted truncated pyramidal shape. However, FIG. 12 shows a substrate84 formed with an array of micro-reflectors 86 having a parabolic shape.AN LED 88 is mounted in each micro-reflector as discussed above so thatlight from each LED 88 is reflected by layer 90. Layer 90 preferably isboth a reflective and electrically conductive layer as discussed above.

The substrate may be formed of any size and the LEDs arranged in anydesired dense configuration required for a particular application.

A dense LED array is also contemplated in which an array ofmicro-reflectors is formed using a substrate of other than silicon. Suchsubstrate may be an insulator, a semiconductor, a conductor, orcombinations of one or more of these or other materials. As examples,the substrate may be glass, ceramic, plastic, diamond, SiC, AlN, BeO,Al2O3, or combinations of these or other materials. Preferably, thesubstrate provides for formation of micro-reflectors, either formed inor on its surface, or some combination of both.

Micro-reflectors may be formed using various technologies. As examples,the micro-reflectors may be formed using lithographical technology,machining, stamping, casting, forging, or other processes, orcombinations of one or more of these. To illustrate, micro-reflectorsmay be formed by machining openings (e.g., via lasers and/or plasma). Tofurther illustrate, micro-reflectors may be formed by a combination ofetching, together with machining or other technology. In this furtherillustration, a substrate is etched to form openings. Each opening isthen machined to a desired shape, such as a parabolic shape. Suchmachining may be performed before or after the substrate, including theopenings, is coated with a reflective material.

FIG. 13 shows an embodiment in which a plurality of micro-reflectors maybe formed by a combination of etching and other processing. Substrate 92is formed with a plurality of micro-reflectors 94 wherein substrate 92is first etched to form openings 96 in a manner discussed above withreference to FIGS. 7-9. A layer of reflective (and, preferably,electrically conductive) material 98 is applied to substrate 92,including in the openings 96. The openings 96 are then processed, e.g.,machined, so as to have a selected shape or shapes. As shown, the shapesare parabolic, but it is understood that other shape(s) may be employed(e.g., faceted). Additional metallization layers may then be applied(e.g., if machining removes undesirable amounts of metal). Furtherprocessing of the openings 96 may be performed (e.g., stamping to formthe desired shape(s) within the openings 96). In doing such additionalprocessing after the etching operation, not only are themicro-reflectors 94 are formed, but also the achievement of the desiredshape(s) of such reflectors tends to be enhanced. A plurality of LEDs100 are then mounted within the micro-reflectors 94 in the mannerdiscussed above.

Although this description focuses on forming openings disposed in aselected substrate, it should be understood that a selected material maybe layered on the surface of the substrate and openings may be formed insuch material, without entering the substrate. It is also contemplatedthat the openings may be formed in such material, while yet entering thesubstrate.

In another embodiment as seen in FIG. 14, directionality of light can befurther improved by molding or aligning a microlens array 102 over anLED array 104 similar to those of FIGS. 7-9, 12, and 13. In thisembodiment, each microlens 106 is associated with a micro-reflector 108to further collect and collimate light from an associated LED 110. Onetype of microlens array is shown and described in PCT Appl. No.PCT/US04/36370, filed Nov. 1, 2004, the contents of which are herebyincorporated by reference in its entirety for all purposes.

The present invention provides for a method of manufacturing an arraymodule in which a substrate is metallized. Electrical circuits arestructured on the metallized substrate and the substrate is etched toform openings. The openings are metallized to form micro-reflectors thatreflect light (and, preferably, that provide electrical connection foran associated semiconductor device). This enables the formation offeatures in the electrical circuit separately from the etching andplating tasks associated with forming the micro-reflectors.

Persons skilled in the art will recognize that many modifications andvariations are possible in the details, materials, and arrangements ofthe parts and actions which have been described and illustrated in orderto explain the nature of this invention and that such modifications andvariations do not depart from the spirit and scope of the teachings andclaims contained therein.

The invention claimed is:
 1. A method for an optical array module,comprising: providing a substrate, forming a plurality of openings inthe substrate, providing a 1-10 micron layer of conductive, reflectivematerial in each opening, and mounting a semiconductor device that emitshighly divergent light in a hemispherical radiation pattern within eachopening wherein the layer of conductive, reflective material in eachopening reflects light from its associated semiconductor device, andwherein the conductive, reflective material electrically connects thesemiconductor device to a power source.
 2. The method of claim 1,wherein the openings in the substrate are formed by an anisotropiccrystallographic etching process.
 3. The method of claim 2, wherein theanisotropic crystallographic etching process is performed along a 1-0-0crystalline silicon axis.
 4. The method of claim 2, wherein eachmicro-reflector is formed in a truncated pyramidal shape.
 5. The methodof claim 1, wherein the openings in the substrate are formed by amachining process.
 6. The method of claim 5, wherein the openings have aparabolic shape.
 7. The method of claim 1, wherein the openings areformed in an array having a center-to-center spacing of about 800microns (0.032 in.).
 8. The method of claim 1, wherein the substrate isformed from one of silicon, SiC, diamond, AlN, Al203, or BeO.
 9. Themethod of claim 1, wherein each semiconductor device has a height andeach opening has a depth, the height of each semiconductor device beingsubstantially equal to the depth of each opening.
 10. The method ofclaim 1, further comprising depositing a dielectric layer and a titaniummetal adhesion layer in that order on the substrate prior to depositingthe conductive, reflective layer.
 11. The method of claim 1, furthercomprising depositing a nickel metal barrier layer on the substrateprior to depositing the conductive, reflective layer.
 12. The method ofclaim 1, wherein mounting the semiconductor device comprises eutecticbonding the semiconductor device.
 13. A method for an LEDmicro-reflector array, comprising: forming a plurality of recesses in asubstrate; providing a dielectric layer, a metal adhesion layer, and abarrier metal layer, in that order, on the substrate; providing anelectrically conductive and optically reflective layer on the barriermetal layer; and mounting a semiconductor device that emits highlydivergent light in a hemispherical radiation pattern within each recesswherein the electrically conductive and optically reflective layer ineach recess reflects light from the corresponding semiconductor device,and wherein the electrically conductive and optically reflective layerelectrically connects the semiconductor device to a power source. 14.The method of claim 13, wherein a thickness of the electricallyconductive and optically reflective layer is 1 micron or more and 10microns or less.